As typical methods of moving a robot toward a target position, a reproduction operation of an operation program and a jog operation are employed. The latter jog operation method comprises a base (world) coordinate system jog, a user coordinate system jog, a tool coordinate system jog, individual axes jog, and the like. These methods are selectively used for various applications.
Of these jogs, the tool coordinate system jog is characterized by that jog operation by translational/rotational moving direction during a jog operation can be specified according to a tool coordinate system defined together with a tool such as a welding torch, a sealing gun, a spot gun, or a hand which are to be mounted on the distal end of the robot. For this reason, this tool coordinate system jog is relatively frequently used in an application such as arc welding or sealing.
For example, in the case of an arc welding robot, as shown in FIG. 1, in many instances, a tool coordinate system such that a distal end 2 of a welding torch (hereinafter referred to as "torch") 1 is defined as an origin, a torch direction is defined as a Z axis, and a direction which frequently corresponds to a torch front is defined as an X axis. It should be noted that the "torch front" means a torch surface, which faces a welding line direction (advancing direction of welding) 3.
When teaching a robot its position for a jog operation conforming to the tool coordinate system defined as described above, at least at the stage of attitude teaching, in general, it is a common practice for an operator to adjust the attitude of the robot after bringing the robot to the position at which the direction of its X-axis coincides with the welding line direction 3. This is because, when one specific coordinate axis (X axis) of the tool coordinate system is made to coincide with the welding line direction 3, operability of the tool aided by the sense of the operator in the subsequent jog operation according to the coordinate system can be improved.
More specifically, the relationship between a jog operation key and the moving direction of the robot (especially, the direction of rotational movement) can be sensed with greater ease in this way. For example, an operator not only can be conscious of a jog key operation for moving around an .+-.X axis in correspondence with rotational movement around the welding line direction 3, but also can be conscious of rotational movement around an axis which is vertical to the welding line direction 3, or vertical to the coordinate axis corresponding to the axial direction of the tool, relating to a jog key operation for moving around a .+-.Y axis. As quantities for describing torch attitudes to be adjusted as described above, a work angle and a travel angle are used.
FIG. 2 is a view for explaining a work angle and a travel angle on an arc welding robot, and shows the relationship among a welding line, a reference surface, a work angle, a travel angle with reference to linear welding paths A and B. Referring to FIG. 2, a reference surface .GAMMA.0 is used as a reference together with the welding line direction (direction of A - B) 3 when the work angle Is defined. In general, a work surface representing a work portion in which the welding path A-B is present is selected as the reference surface .GAMMA.0. Reference symbol &lt;n&gt; denotes a normal vector representing the direction of the reference surface .GAMMA.0, and reference symbol .GAMMA.1 denotes a surface which is vertical to the reference surface .GAMMA.0 with respect to the path A-B being a cross line. In this case, it must be noticed that the reference surface .GAMMA.0 is used only to define the work angle.
When a plane .gamma. on which a straight line representing the direction (Z-axis direction of the tool coordinate system) of a torch 1 and the welding line A-B are placed is considered, an angle between the plane .gamma. and the reference plane .GAMMA.0 is a work angle .theta.. Also, when a vertical line g extending from a tool center point 2, and vertical to the welding line A-B, is set on the plane .gamma., an angle between a straight line representing the direction (Z-axis direction of the tool coordinate system) of the torch 1 and the straight line g is a travel angle .PHI.. Thus, the work angle .theta. is an angle around the welding line A-B, while the travel angle .PHI. is an angle around the vertical line g extending from the welding line A-B on a reference plane (work surface) .GAMMA.0.
For example, in fillet welding, an attitude having, as the work angles .theta., an angle which divides two work surfaces is taught. However, if the torch 1 (or its welding wire portion) is brought close to the work surface, a phenomenon such as undercut, overlap, or the like may be caused due to uneven heat transmission. Furthermore, when the travel angle .PHI. is excessively increased to smooth a bead shape, a so-called lack of penetration phenomenon occurs. As is apparent from this example, a torch attitude (in general, robot attitude), defined by the work angle .theta. and travel angle .PHI., is an important factor which determines the quality of the operation such as a welding operation or sealing operation.
Thus a torch attitude to be defined by a work angle and a travel angle must be taught accurately. For this reason, in an actual position teaching operation, a careful operation must be performed to adjust the work angle and the travel angle at each teaching point. As described above, when the X-axis direction of the tool coordinate system is made to coincide with a welding line direction (direction of the path A-B in FIG. 2), the work angle can be adjusted by a jog operation around the X axis and adjustment of the travel angle, by the jog operation around Y-axis.
In practice, however, it is often difficult to make the X-axis direction of the tool coordinate system coincide with the welding line direction by the positional relationship between a work having various shapes and the robot. In order to overcome such difficulty, there is a method in which, in place of the X-axis direction, the Y-axis direction is made to coincide with the welding line direction, the work angle is adjusted by a jog operation around the Y axis, while the travel angle is adjusted by a jog operation around the X axis. In this case, it is necessary to depress a jog key which is different from one to be depressed in a normal case wherein an attitude is adjusted when the X-axis direction and the welding line direction are made to coincide with each other.
Furthermore, according to circumstances, there may be a case where it is difficult for both the X-axis direction and Y-axis direction to be made to coincide with the welding direction. In such a, case, the jog operation around the X-axis direction and the jog operation around the Y-axis direction need to be combined to adjust the work angle and the travel angle. Such adjustment procedure, however, not only requires a high-degree of skill but also requires an extremely long time for teaching operation.
As described in the foregoing taking an example of a welding robot, the jog operation based on a conventional tool coordinate system is carried out according to a coordinate system corresponding to the attitude of a wrist of the robot, so that it is effective in teaching a path position of a robot which has a wrist to which a tool (a welding torch, a sealing gun, a spot gun, a hand, or the like) is attached. In particular, as described in the foregoing taking an example of the welding torch, the conventional jog operation method provides an effective means when an attitude of a tool relative to a work has to be correctly taught.
However, in some cases, it may be difficult to shift to an adjusting operation of a work angle so as to teach an attitude, while making one specific axis (X axis) of the tool coordinate system to coincide with the direction of a welding line (in general, an operation line; for example, a sealing line in the case of a sealing robot). More specifically, in case where the work angle and the travel angle need to be adjusted with an axis (Y axis) other than the above-specified axis (X axis) made to coincide with the direction of the operation line, this gives rise to a problem such that a jog operation different from conventional one is required. Furthermore, when it is difficult for both the X and Y axes to be made to coincide with the direction of the operation line, a more cumbersome jog operation is required.